It is considered that sordes formation is an important cause of tooth decay. Namely, there is a convincing hypothesis in which tooth decay may proceed by converting sucrose in food to viscous polysaccharide glucan by glucosyltransferase which is an extracellular enzyme of Streptococcus mutans, so that the glucan adheres to the tooth to form sordes, resulting in decrease of pH of tooth surface by organic acids produced by microorganisms which proliferate in the sordes, resulting in destruction of the enamel portion. There are proposed as a method for preventing tooth decay a method for inhibiting sordes formation, a method for preventing acid production by microorganisms in sordes, or a method for decomposing and removing formed sordes.
Since the causing substance of sordes formation is glucan, it is necessary for reducing sordes formation to reduce glucan formation. For this purpose, several substances are conventionally proposed as substances for inhibiting sordes formation. For example, a sordes inhibiting agent comprising flavonoid is disclosed in Japanese laid-open patent application No. 59-13721, a sordes inhibiting agent composition containing chitin or chitosan is disclosed in Japanese laid-open patent application No. 61-151112, a composition for oral cavity containing .gamma.-linolenic acid and/or linoleic acid having a tooth decay preventing effect is disclosed in Japanese laid-open patent application No. 61-260017, and a composition for oral cavity containing a seed oil of evening primrose is disclosed in Japanese laid-open patent application No. 61-268613.
It is ideally more desirable for a sordes formation inhibiting substance to be extracted from natural sources, especially from food materials which are anciently used as food to be acknowledged safe for human body, from a view of safety, than synthesized substances. Moreover, it is necessary for using that a composition used in the oral cavity have a good taste. Alternatively, even if a sordes formation inhibiting substance is extracted from natural substances those whose source is a natural substance that is different to obtain or requires a complex purification process has a problem of cost and is inconvenient to utilize industrially. Conventional materials for oral cavity which have an effect of inhibiting sordes formation do not fully satisfy all these requirements, among which obscure effects are provided, so that it is desired to develop a material for oral cavity which has more ideal effect for inhibiting sordes formation and to realize a composition for oral cavity containing it.